Add a trigger in a ftplugin script

[Rmano]

Hi. I am using which-key using this configuration in mu init.vim:

[...] configuration for VimPlug removed
"
" which-keys
"
Plug 'folke/which-key.nvim'
"
call plug#end()
"
" which-key
"
lua << EOF
require"which-key".setup{
        preset = "helix",
        triggers = {
             { "<auto>", mode = "nxso" },
             { "`", mode = "i" }, -- for VimTeX, no way to put it into tex.lua
        },
}
EOF

where I'd like the extra trigger only for TeX mode. Now, I have in ftplugins/tex.lua the following (from here)

local wk = require("which-key")
wk.add({
  buffer = BUFFER, -- e.g. ev.buf or similar
  { -- Vimtex ` shortcuts
          mode = { "i" },
          { "`", group = "Vimtex ` " },
-- more here
  },
  {
    "<localleader>l",
    group = "VimTeX",
    icon = { icon = "", color = "green" },
    mode = "nx",
  },
  {
    mode = "n",
    {
      "<localleader>ll",
      "<plug>(vimtex-compile)",
      desc = "Compile",
--
-- [...] rest removed

What I'd like to do is to add the

{ "`", mode = "i" } 

trigger here, so that it is enabled only for the filetype tex... but I was unable to do it.

Is there any way of doing it?

BTW, happy holiday season to everybody!!!